1. Field of the Invention
The invention relates to the use of antimisting additives for reducing the formation of aerosol in crosslinkable silicone coating compositions.
2. Description of the Related Art
A trend within the silicone coating industry is to increase machine speed in order to raise productivity. Where silicone coatings are applied to the substrate at relatively high speeds, of more than 300 m/min, for example, fine spray mists of the silicone coating system may be formed. This aerosol is formed at the silicone applicator unit. The formation of this spray mist proves to be a serious problem in the context of further increasing the coating speed.
The formation of this spray mist can be reduced by adding what are known as antimisting additives to the silicone coating system.
EP-A 716 115 (Dow Corning Corp.) and the corresponding U.S. Pat. No. 5,625,023, U.S. Pat. No. 5,698,655 and U.S. Pat. No. 5,994,454 describe anti-misting additives obtained by reacting an organosilicon compound, a compound containing oxyalkylene groups, and a catalyst. The addition of these oxyalkylene-functional reaction products to crosslinkable silicone coating systems reduces the formation of aerosol in rapid coating operations.
WO 01/98420 (Dow Corning Corp.) discloses a liquid silicone antimisting composition obtained by reacting                (a) an organohydropolysiloxane containing at least 2 Si—H groups (SiH) with        (b) an organoalkenylsiloxane containing at least 23 alkenyl groups (C═C) in        (c) the presence of a platinum catalyst and if desired of        (d) an inhibitor.        
An extremely large excess of organoalkenylsiloxane is necessary in order that no gelling occurs. This excess of organoalkenylsiloxane of relatively high functionality, which, moreover, is complicated to synthesize, has a considerable effect on the release properties of the base system, the crosslinkable silicone coating composition. Additionally it is necessary to add an inhibitor in order to prevent gelling.
U.S. Pat. No. 6,034,225 (Wacker-Chemie GmbH) describes alkenyl-functional siloxane polymers which are branched and whose organopolysiloxane blocks are linked by hydrocarbon bridges.